This invention generally relates to intravascular catheters, particularly dilatation catheters for percutaneous transluminal coronary angioplasty.
In typical PTCA procedures, a guiding catheter having a preshaped distal tip is percutaneously introduced by conventional Seldinger techniques into the vascular system of a patient and advanced within the system until the preshaped distal tip of the guiding catheter is disposed within the ascending aorta adjacent the ostium of the desired coronary artery. The guiding catheter is relatively stiff because it has to be twisted or torqued from its proximal end, which extends outside the patient, to turn the distal tip of the guiding catheter so that it can be guided into the desired coronary ostium. A balloon dilatation catheter is introduced into and advanced through the guiding catheter and out the distal tip thereof into the patient""s coronary artery until the balloon on the distal extremity of the dilatation catheter is properly positioned across the lesion to be dilated. Once properly positioned, the balloon is inflated one or more times to a predetermined size with radiopaque liquid at relatively high pressures (e.g., generally 4-12 atmospheres) to dilate the stenotic region of the diseased artery. When the dilatations have been completed, the dilatation catheter can be removed from the dilated stenosis to allow the resumption of blood flow through the dilated artery.
There are several types of balloon dilatation catheters which are now widely available, including over-the-wire catheters, fixed-wire catheters, rapid exchange type catheters (which are a type of over-the-wire catheter) and perfusion type catheters (which may be either over-the-wire or rapid exchange type catheters).
Commercially available dilatation catheters typically have balloons with working lengths of 2 cm. Longer balloons, e.g. 3 and 4 cm, have become available in the marketplace to dilate longer lesions so that multiple dilatations along the length of the lesion are not necessary for complete dilatation. However, this increases the number of catheters which must be kept available during a dilatation, because frequently it is not known before the procedure begins how long the lesion is.
Saab in U.S. Pat. No. 5,246,421 discloses an elongated sheath which extends over a long balloon and is adjustable therewith so that only a desired length of balloon which extends distally out of the sheath expands when the balloon is inflated. However, as described, the elongated sheath extends along most of the catheter length, adding both to the profile and the stiffness of the catheter assembly. What has been needed and heretofore unavailable is a dilatation catheter with an adjustable length balloon which does not significantly increase the profile and stiffness of the catheter assembly over the profile and thickness of commercially available products. The present invention satisfies this and other needs as will be described hereinafter.
The present invention is directed to a dilatation catheter assembly which provides a low profile, flexible dilatation balloon with a variable working length to accommodate a wide variety of stenotic lengths.
The dilatation catheter assembly of the present invention has a dilatation catheter with an elongated shaft, a dilatation balloon on a distal portion of the shaft and a relatively short balloon sheath which is securable at a desired location on the catheter shaft with the sheath extending over a part or all of the dilatation balloon. The short balloon sheath is secured at the desired position on the catheter shaft before it is introduced into the patient. The desired sheath position is selected so that the sheath extends over the balloon to prevent a length of the balloon which is covered by the sheath from expanding when inflation fluid is introduced under pressure into the interior of the balloon, but a length of the balloon which extends out the distal end of the sheath, i.e. is uncovered, is expanded when inflation fluid is introduced into the balloon interior. The length of exposed balloon is usually chosen to correspond to, or overlap the length of the lesion to be dilatated.
The elongated catheter shaft has proximal and distal ends, a first inner lumen extending within at least a distal portion of the catheter shaft to a guidewire port in the distal end of the shaft, a second inner lumen extending from the proximal end of the shaft to a location spaced proximally from the distal tip of the shaft and in fluid communication with the interior of the inflatable dilatation balloon on the distal portion of the catheter shaft.
The balloon sheath has an inner lumen extending along the length thereof with a distal extremity configured to envelop a desired length of the inflatable dilatation balloon in a deflated condition. Preferably, the inner lumen of the distal extremity of the sheath is sufficiently long to cover at least one-half, and preferably the entire working length of the balloon, i.e. the cylindrical portion of the balloon between the balloon tapers and has sufficient diameter to readily receive the balloon in a deflated condition. The sheath/dilatation catheter assembly is configured so that initially the sheath and the dilatation catheter are longitudinally moveable with respect to each other, but means are provided to fix the position of the sheath with respect to the catheter when the assembly is outside the patient so that the desired length of balloon can be exposed before insertion into the patient, but in a manner so that the sheath will resist movement during advancement within the patient""s vasculature or during the intravascular procedure.
A variety of means may be employed to secure the sheath with respect to the catheter. For example, the sheath may be configured to have a friction fit with the catheter shaft or the balloon or both of a magnitude which allows manual movement before the procedure but which prevents movement within the patient from frictional forces to which the device is subjected therein. Other means include bonding the proximal portion of the balloon sheath to the catheter shaft after the sheath is in the desired position by the use of an adhesive, by fusion bonding (heat or laser) or by mechanical bonding. Additional means include shaping the inner lumen of the sheath and the exterior or the catheter shaft so that rotation of one of the members with respect to the other will result in a frictional fit therebetween, e.g. both being oval shaped. A variety of other means can be employed for fixing the position of the sheath with respect to the catheter so as to expose a desired length of the dilatation balloon which will expand when inflated but to cover a length of the dilatation balloon which will not expand when the balloon is inflated. The means for fixing the position of the balloon must be functional after the sheath is placed in the desired position but before the assembly is introduced into the patient""s vasculature.
The sheath which extends over the balloon should have sufficient strength to prevent the portion of the dilatation balloon over which it extends from expanding. Generally, the sheath can be made of high strength polymer materials such as high density polyethylene, polyethylene therephthalate, ionomers and other materials from which dilatation balloons are made. The sheath should not, however, be so stiff that it detrimentally effects the tracking of the dilatation catheter over the guidewire which the catheter is advanced through the patient""s coronary artery. The distal end of the sheath may be provided with a short elastically expandable element which expands to the shape of the proximal end of the expanded balloon portion.
One way of providing the sheath with sufficient longitudinal flexibility, so that tracking of the catheter is not impaired while maintaining sufficient radial rigidity to prevent expansion of the sheath when the balloon is inflated, is to provide, along the length of an otherwise flexible, elastic sheath which is to cover the balloon, a plurality of longitudinally spaced circular bands which are made of high strength relatively inelastic polymer material such as biaxially oriented polyethylene terephthalate. The length of the sheath for the most part remains as longitudinally flexible as without the bands, but the bands effectively prevent significant radial expansion of the portion of the balloon which is covered by the sheath.
Another way to provide the sheath with longitudinal flexibility and radial inelasticity is to form the sheath out of flexible or elastic polymeric material with reinforcing inelastic strands within the matrix of the polymeric material which provide a minimum expansion to an otherwise elastically expandable sheath. The inelastic reinforcing fibrous strands may be braided, wound or otherwise positioned within the polymer matrix to restrict the radial expansion thereof.
The catheter assembly of the invention is used in essentially the same manner as a conventional dilatation catheter, with the assembly being advanced through a guiding catheter which has its distal end seated within the desired coronary ostium and out the end of the guiding catheter into the patient""s coronary artery until the distal end of the assembly is disposed proximal to the stenosis to be dilated, as described in the BACKGROUND OF THE INVENTION. The length of the stenotic region is determined by angiography or other means before the angioplasty catheter is inserted into the patient so that the length of exposed working surface of the dilatation balloon can be adjusted according to the length of the stenosis to be dilated. The catheter assembly is then advanced through the guiding catheter and out the distal end thereof into the desired coronary artery until the exposed portion of the dilatation balloon is disposed within the stenotic region so that, when it is inflated, essentially the entire length or at least a much greater length of the stenotic region is dilated.